Differential measuring gauge



1952 D. N. KIRKPATRICK 2,584,714

DIFFERENTIAL MEASURING GAUGE Filed June 21, 1949 AMPLIFIER DETECTORAMPLIFIER DETECT R INVENTOR 004M117 A! K/AAPA 7' 14 /6 A ATTORNEYSPatented Feb. 5, 1952 i UNITED STATES PATENT OFFICE DIFFERENTIALMEASURING GAUGE Donald N. Kirkpatrick, Livingston, N. J., assignor I toFederal Products Corporation, Providence, 7

Application June 21, 1949, Serial No. 100,391

8 Claims.

The present invention relates to improved and simplified differentialmeasuring apparatus and moreparticularly to apparatus for indicatingautomatically whenever a workpiece is out-ofround by more than apredetermined maximum.

This invention provides ahighly-stable, easilyoperated system forindicating automatically when the out-of-round" of a workpiece exceeds apredetermined adjustable maximum, and in which such indications aresubstantially independent of themean diameter of the workpiece. Theapparatus has the advantage that it is relatively low in cost andreliable in operation so that a minimum amount of service attentionisrequired, and the measuring accuracy is not affected substantially bychanges in supply voltage such as ordinarily occur in commercialinstallations. The invention accordingly consists in the variousfeatures of construction and combinations of mechanical apparatus andelectronic circuits as will be exemplified in the structure to mostimportance to know which of the parts exceeds a given tolerance limit,and that the measurement be substantially independent of the meandiameter of the workpiece. For example, in high speed production, partsthat are fabricated on centerless grinders usually develop a three-lobedconfiguration. If the maximum amount of out-of-round, based on thethreelobed configuration, is determined in accordance with theparticular requirements of the application for which the parts areintended, the apparatus shown in the figure can be adjusted to indicateOr reject all pieces which have an outof-round measurement exceedingthat amount. In accordance with this invention, such measurements can bemade rapidly, accurately, and automatically so that the cost permeasured unit is extremely low.

As shown in the figure, a workpiece 2 rests in a 90 degree V-bed 4 andis arranged to be rotated on the V-bed and to be moved longitudinallytherealong by suitable driving wheels (not shown).. A- first gauge head6, havinga move-1 able feeler 8,. engages the-surface of the WOIk'.piece 2 and, in this example, is inclined at an. angle of 30 degreesfrom-- the vertical center-line til, the feeler -8 being directedsubstantially toward the center of workpiece 2. A second gauge head [2,having afeeler 14 also engaging the surface of the workpiece-2, isinclined at an angle of 30 degrees in the opposite direction from thevertical center-line ID. The gauge heads 6 and 52 are connected,respectively, to amplifier and detector arrangements shown in block format HiandlB.

Thegauge heads '6- and -I2 and the amplifier and'de-tector arrangementsl6 and I8, may, for example, be of the general type described in pat entapplication Serial No. 541,201, filed June 20, 1944, by Harold A; Snow,now U. S. Patent 2,503;-

851, and the positioning of the gauge heads B'and I2 with respect to theworkpiece and the V-bed may be substantially as shown, or in accordancewith technique not herein important to the subject matter of the presentclaims.

As described in said patent, a direct voltage is developed betweenoutput terminals 22 and 24 of amplifier-detector arrangement I6 which isa function of the displacement of the feeler 8, from a neutral position,with respect to the gauge head -6. In a similar manner, a direct voltageis devloped between output terminals 26 and 28 ofamplifier-detectorarrangement [8 which is a funcn tion of the displacement of the feeler I4, from its neutral position, with respect to gauge head l2.

The direct voltage appearing at terminallzl is connected throughanisolating resistance 32 to .a control grid '34 of a triode vacuum tube36, a grid return circuit being provided through .a

resistance 38. Cathode 42- of this tube is returned to ground through afixed resistance42 and an'adjustable tap 46 of a potentiometer 48.

Anode 52 of this tube is connected to positive -.terminal '56 of aconventional power supply..'

shown in block form at-58.

The'voltage appearing at terminal 22 'of the amplifier detector l6, ofpositive polarity'in this example, controls the magnitude of thecurrentflowing through tube 36'. Therefore, the voltage developedbetween cathode 42 and ground is a function of the magnitude of thispositive control voltage.

Terminal 26 of amplifier detector I8 is conj nested through an isolatingresistor '62 to a control grid 84 of a triode vacuum tube 88 (preferablyidentical with tube 38), a ground return circuit being provided througha resistance 88. Cathode I2 of tube 88 is connected to ground through aresistance I4 and the adjustable tap 48 of potentiometer 48. Anode 18 ofthis tube is connected to the positive power supply terminal 58. Theplate current that flows through tube 88, and accordingly the voltage atcathode I2. is a function of the magnitude of the positive voltageappearing at terminal 28 of amplifier detector I8.

The voltage appearing at cathode 42 is connected through an adjustabletap 82 of potentiometer 84 to a control grid 88 of a gaseous dischargetube 88. A negative bias voltage, the magnitude of which can be variedby adjustment of the tap 82 of potentiometer 84, is provided by abattery 92 connected in parallel with the potentiometer 84. The voltageappearing at cathode 42 is'positive with respect to ground so'that thegrid bias'voltage' provided by battery 82 is opposed in polarityto thesignal voltage provided from the cathode 42.

Cathode 84 of gaseous discharge tube 88 is connected to cathode I2 oftube 88. Anode 98 of gaseous discharge tube 88 is coupled through acurrent-limiting resistor 98, relay actuating coil I82 01' a relay I04,a series resistor III5, and contact I08 and armature I88 of a relay II2to positive terminal 58 of power supply 58'. A condenser II3 isconnected from the junction of resistor I05 and coil I82 to ground; andforms, in conjunction with a resistor I85, filter or timedelay networkwhich prevents ignition of the tube 88 by transient or shock signalswhen the anode voltage is re-applied suddenly.

The voltage appearing at grid 88' with respect to ground is a functionor the voltage delivered by amplifier-detector I8, whereas the voltageappearing at cathode 84 of tube Wis 13. function of the magnitude ofvoltage delivered by ampliher-detector I8. So long as the voltage ongrid 88 of tube 88 is negative by a predetermined amount with respect tocathode 84, tube 88 will not ignite, but if the relative positivevoltage on grid 88 exceeds this predetermined amount, the tube 88 willignite and carry substantially full current until de-energized by someexternal means. As the magnitude of the voltage from amplifierdetectorI8 increases, the anode current through tube 38 increases, thusincreasing the voltage of grid'88 of tube 88 in a positive direction,which would tend to cause the tube 88 to ignite and to carry current. Asthe magnitude of the voltage delivered by amplifier-detector I8increases, the anode current of tube 88 is increased, which increasesthe potential of cathode 84 in a positive direction, thus, tending toprevent the ignition of tube".

In operation, the potentiometer 48 is adjusted so that tubes 38 and 88carry equal plate currents with equal voltages applied to their controlgrids.

If a right or true cylindrical workpiece is rotated on the V-bed 4, thevoltage delivered by amplifier-detector I8 will be the same as'thevoltage delivered by amplifier I8, and, accordingly,

the plate currents of tubes 38 and 85 will be equal, and the voltagesapplied to the grid 88 and cathode 94 of tube 88 will effectivelyofl'set one another, so that only the residual negative bias applied bybattery 92 will be effective and, if this voltage is adjusted so that itis more negative than the critical value, tube 88 will not ignite. Inpractice, tap 82 of potentiometer 8H8 adjusted so that the tube will notignite unless a greater positive voltage is applied to the grid than isapplied to the cathode, and furthermore so that this difference involtage required to ignite the tube 88 represents the diil'erence involtage produced as a result of a difference in out-of-roundcorresponding to the desired tolerance limit. For example, assume that aworkpiece having an out-oi-round exceeding the maximum desired tolerancelimit is rotated on the V-bed 4, the difierence in the voltagesdelivered by amplifierdetectors I8 and I8 will vary as the workpiece isrotated. At one point during the rotation, terminal 22 will be morepositive than terminal 28 by the maximum amount. At this point, thepositive voltage applied to grid 88 of tube 88 will not be entirelyoffset by the positive voltage applied to cathode 84, by virtue of thevoltage existing at terminal 28 and, because the workpiece 2 exceeds thedesired dimensional limit, the gaseous tube 88 will ignite and carrysubstantially full plate current.

When tube-88 ignites, actuating coil. I82 of relay I84 is energized andarmatures I I4 and I I8 will. be drawn inwardly toward the core of coilI82. This movement causes armature M4 to engage relay contact II8, whichcloses a circuit from power supply terminal 56 through armature I I4,contact II8, resistance I22, and a reject indicator lamp 2:24 to ground.This circuit ignites the indicator lamp I24 denoting that the workpieceunder test should be rejected. A terminal I28 is also provided which isenergized simultaneously with lamp I24 and which may be utilized tooperate auxiliary relays and other apparatus to automatioally reject theworkpiece. If the tube 88 fails to be ignited by the workpiece undertest, relay coil I02 remains tie-energized and the circuit is completedfrom power supply terminal 58 through armature II4, dropping resistanceI28, and lamp I32 to ground, indicating that the workpiece under test iswithin the prescribed tolerance limit.

The ignition of tube 88 also initiates the action of a time-delaycircuit for extinguishing the tube 88 so that another workpiece can betested. In order to accomplish this, a vacuum tube I84 is provided, thecathode I38 of which is connected to ground, and the anode I42 of whichis connected to power supply terminal 58 through actuating coil I44 ofrelay II2. Control grid I46 of this tube is ordinarily biased negativelyby means of a battery I48 which is connected to grid I48 through aresistance I52, the positive terminal of the battery being connected toground. The grid I46 is also returned to ground through a parallelresistance 554. This negative bias supplied to grid I48 preferably issufficient to substantially limit the flow of plate current in tube I34so that relay coil I44 is not suillciently energized to at tractarmature Hi8.

The negative bias applied to the grid I46 charges a condenser I58 and acondenser I5! which is connected in parallel with condenser I58 througha normally-closed switch I50, the condensers being connected betweengrid I46 and ground. However, when tube 88 is ignited, and actuatingcoil I82 of relay I84 is energized, a circuit is closed from groundthrough relay contact I58, armature HE, and resistance I62 to the gridI48. The change in bias voltage of tube I34 caused by completion of thiscircuit will cause an increase in the plate current of tube I34, butthis effect cannot take place instantaneously because of the timerequired to discharge the con densers I58 and I51. Accordingly, thebias-voltage on grid I46 will gradually become less negative, at a ratedependent upon the values of the resistors and condenser in the gridcircuit. These circuit values are selected to provide a time constant,or period of delay, depending upon the rate at which it is desired totest the individual pieces. As the grid I46 becomes increasinglypositive, the anode current through tube I34 increases until relayactuating coil I44 is sufilciently en- In order to facilitate thesetting-up of the instrument, the switch I60 is opened so that thecycling rate is controlled only by condenser I55, which is much smallerthan condenser I51 and thus causes rapid cycling so that the indicatorlamps will follow rapid changes in the positions of the feelers 8 and I4or adjustment of contact 82 of potentiometer 84.

It is apparent that the apparatus described herein is well suited toobtain the ends and objects hereinbefore set forth, and that certainoperating advantages, particularly valuable in the practicalinstallations, are inherent in the ar- 1- tively is cancelled. Thefiring-point of gaseous discharge tube 88 will not be affected adverselyby normal line voltage changes because of the inherent characteristicsof such tubes.

I claim:

1. A diiferential measuring system for indicating automaticallyworkpieces having an out-ofround exceeding a predetermined limitcomprising first and second gauge heads having movable feelers adaptedto engage at spaced positions the surface of a rotating workpiece, firstand second amplifier detectors coupled, respectively, to said first andsecond gauge heads for producing first and second direct voltages whichare functions, respectively, of the displacements of the feelers of saidfirst and second gauge heads with respect to their neutral positions,first and second electron amplifier tubes coupled, respectively, to saidfirst and second direct voltages and having their anode currentscontrolled thereby, a relay con trol tube coupled to said first andsecond tubes and having a first control electrode coupled to said firsttube and a second control electrode coupled to said second tube soarranged that an increase in anode current of said first tube tends toincrease the current through said relay control tube and an increase inanode current of said second tube tends to decrease the current throughsaid relay control tube operatively to respond only to a difierential involtage supplied from said first and second amplifier-detectors, a relaycontrolled by the current through said control tube, and an indicatorcircuit energized. by said relay in response to measurement of aworkpiece having an out-of-round greater than said predetermined limit.

2. A differential measuring system for indicating automaticallyworkpieces having an out-ofround exceeding a predetermined limitcomprising first and second gauge heads having movable feelers adaptedto engage at spaced positions the surface of a rotating workpiece, firstand second amplifier-detectors coupled, respectively, to said first andsecond gauge heads for producing first and second direct voltages whichare functions, respectively, of the displacements of the feelers of saidfirst and second gauge heads with respect to their neutral positions,first and second vacuum tubes each having an anode, a cathode, and acontrol electrode, each of said control electrodes being coupled to oneof said direct voltages so that the anode currents of said tubes are controlled thereby, a gaseous discharge control tube coupled to said firstand second tubes and having a first control electrode coupled to saidfirst tube and a second control electrode coupled to said second tubeand arranged so that an increase in anode current of said first tubetends to ignite said control tube and an increase in anode current ofsaid second tube tends to prevent ignition of said control tubeoperatively to respond only to a differential in voltage supplied fromsaid first and second amplifier-detectors, a relay controlled by thecurrent through said control tube, and an indicator circuit energized bysaid relay in response to measurement of a workpiece having anout-of-round greater than said predetermined limit.

3. A differential measuring system for indicating automaticallyworkpieces having an out-ofround exceeding a predetermined limitcomprising first and second gauge heads having movable feelers adaptedto engage at spaced positions the surface of a'rotating workpiece, firstand second amplifier-detectors coupled, respectively, to said first andsecond gauge heads for producing first and second direct voltages whichare proportional, respectively, to the displacements of the feelers ofsaid first and second gauge heads with respect to their neutralpositions, first and second amplifier vacuum tubes having input, andoutput circuits, said input circuits being coupled, respectively, tosaid first and second direct voltages and having their anode currentscontrolled thereby, a gaseous discharge control tube, coupling circuitsso coupling said output circuits to said control tube that the voltagesfrom said output circuits effectively oppose each other, a relayconnected in series with said control tube, an indicator energized bysaid relay for denoting the presence of a workpiece having anout-of-round greater than said predetermined limit, and a time delaycircuit responsive to ignition of said control tube for ole-energizingsaid tube after a predetermined time interval.

4. A differential measuring system for indicating automaticallyworkpieces having an out-ofround exceeding a predetermined limitcomprising first and second gauge heads having movable feelers adaptedto engage at spaced positions the surface of a rotating workpiece, firstand second amplifier-detectors coupled, respectively, to said first andsecond gauge heads for producing first and second direct voltages whichare proportional, respective y, to the displacements of the feelers ofsaid first and second gauge heads with respect to their neutralpositions, first and second amplifier vacuum tubes having input andoutput circuits, said input circuits being coupled, rcspec-- tively, tosaid first and second direct voltages and having their anode currentcontrolled thereby, a gaseous discharge control tube, coupling circuitsso coupling said output circuits to said control tube that the voltagesfrom said output circuits efiectively oppose each other, a relayconnected in series with said control tube, an indicator onergised bysaid relay for denoting the presence of a workpiece having anout-of-round greater than said predetermined limit, and a time delaycircuit responsive to ignition of said control tube for deenergizingsaid tube after a predetermined time interval, said circuit including atleast two condensers and a switch arrange to connect and disconnect atleast one of said CC'HdSIlSulS to said circuit thereby to control saidtime interval so that it can be shortened to facilitate adjustment orcalibration of the system.

5. A differential mcasur'ng system for indicat ing automaticallyworkpieces having an out-ofround exceeding a predetermined t comprisingfirst and second gauge heads has" a to orally-conducting vacuum anode, acathode, and a contro said control electrodes being coup said directvoltages so that the anode C. of said tubes are controlled thereby, asource of anode voltage for ene'gizing said tubes, a nor mallynon-conducting g seous dischar e cont tube coupled to said first andsecond having a first control electrode first tube and a second controlelectrode co ied to said second tube and so arranged that an increase inanode current said first tube tends to ignite said control tube and anincrease in anode current of said second tube tends to vent ignition ofsaid control tube, a source of bias voltage connected to sa d controltube, means for manually varying said bias voltage to regulate theignition point of said control tube, a r lay actuated by ignition ofsaid control tube. a delay circuit actuated by said relay forextinguishing said control tube a predetermined interval of time afterignition thereof, and a control circuit energized by ignition of controltube to indicate the presence of a workpiece exceeding saidpredetermined limit.

A differential measuring system for indicating automatically workpieceshaving an out-of round exceeding a predetermined limit co DliS- ingfirst and second gauge heads having movable feelers adapted to engage atspaced positions the surface of a rotating workpiece, first and secondamplifier-detectors coupl d, respectively, to said first and secondgauge heads for producing first and second direct i 2,16 proper-- 7tional, respectively, to the of tlo feelers of said first and secondgauge eads respect to their neutral positions, first and seccn amplifiervacuum tubes having input and outpu" circuits, said input circuits beingcoupled, respectively, to said first and second direct voltages andhaving their anode currents controlled thereby, a gaseous dischargecontrol tube, coupling circuits so coupling said output circuits to saidcontrol tube that the voltages from said output circuits efiectivelyoppose each other, a first relay connected in series with said controlrelay tube, an indicator energized by said relay for denoting thepresence of a workpiece having an out-of-round greater than saidpredetermined limit, a time delay circuit responsive to ignition of saidcontrol tube for de-energizing said tube after a predetermined timeinterval, and a second relay under the control of said time delaycircuit for re-energizing said tube a predetermined interval of timeafter de-energization thereof.

'7. A differential measuring system for indicating automaticallyworkpieces having an out-ofround exceeding a predeterminedlimitcomprising first and second gauge heads having movable feelersadapted to engage at spaced positions the surface of a rotatingworkpiece, first second amplifier-detectors coupled, respectively, tosaid first and second gauge heads for producing first and second directvoltages which are proportional, respectively, to the displacements ofthe feelers of said first and second gauge heads with respect to theirneutral positions, first and second amplifier vacuum tubes having inputand output uits, said input circuits being coupled, respectively, tosaid first and second direct voltages and having their anode currentscontrolled thereby, a gaseous discharge control tube, coupling circuitsso coupling said output circuits to said control tube that the voltagesfrom said output circuits efiectively oppose each other, a firs u relayconnected in series with said control relay tube, indicator energized bysaid relay for denoting the presence of a workpiece having anout-ofround greater than predetermined limit, a time delay circuitresponsive to ignition of said control tube for de-energizing said tubeafter a predetermined time interval, said circuit including at least twocondensers and a switch arranged to connect and disconnect at least oneof said condensers to said circuit thereby to control said time intervalso that it can be shortened to facilitate adjustment or calibration ofthe s stem, and a second relay under the control of said time delaycircuit for re-energizing said tube a prcdetermined interval of timeafter de-energization thereof.

8. Apparatus for determining when the out-ofround of a workpiece exceedspredetermined limits comprising a workpiece, means for rotating saidworkpiece, first and second gauge heads having movable feelers engagingthe surface of said workpiece, first and second amplifier-detectorscoupled, respectively, to said first and second gauge heads and forproducing direct control voltages proportional in magnitude to thedisplacements of said feelers from their neutral positions, first andsecond vacuum tubes each having a cathode, an anode, and a controlelectrode, said control electrodes being coupled, respectively, to saidfirst and control voltages, a gaseous discharge tube having a cathode,an anode, and a control electrode, first coupling circuit connectingsaid cathode of said first tub-c to said control electrode of saidgaseous discharge tube, a second coupling circuit connecting saidcathode of said second tube to said cathode of said gaseous dischargetube, a source of bias volt age for said gaseous discharge tube, meansfor manually adjusting said bias voltage to prevent 2,684,714 9 l0ignition of said gaseous discharge tube so long n 4 as the currentsthrough said first and second CITED tubes are equal, a first relayresponsive to igni- The following references are of record in the tionof said gaseous discharge tube, an indicator 518 t111$ paienti lampcontrolled by said relay for denoting that 5 the dimensions of saidworkpiece exceed said pre- UNITED STATES PATENTS determined limit, and atime delay circuit under Number Name Date the control of said relay forextinguishing said 2,329,048 Hullegard Sept. 7, 1943 gaseous dischargetube a predetermined interval 2,387,444 Hayslett et a1. Oct. 23, 1945 oftime after ignition thereof. 10 2,417,292 Coake Mar. 11, 1947 DONALD N.KIRKPATRICK. 2,483,867 Anderson et al Oct. 4, 1949

